A common name for a Limited Time Dungeon (or LTD) that is especially used by Japanese players. Guerrilla dungeons are time-restricted dungeons that are only available for a few hours during the day. Examples of these dungeons include rare descends of valuable evolution monsters such as Zeus Dragon or Diara or resource dungeons like Gem Temple or Super Points Cave!
A list of Guerrilla Dungeons that appear for the day can be seen on the main page of this blog or by selecting the LTD Button at the top of the screen in-game.